Resonant Soft-Switching Current Source Inverters for Lower EMI
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Solution Overview
Problem
Conventional voltage-source inverters (VSIs) for variable speed motor drives face issues such as high power density limitations, large short-circuit currents, electromagnetic interferences, and motor losses, while current source inverters (CSIs) suffer from higher conduction losses and lower efficiencies, making them less preferred despite their advantages.
Innovation Solution
The development of soft-switching current source inverters (SSCSIs) that incorporate a first and second CSI bridge, a DC-link inductor, and a resonant tank, enabling bi-directional power flow, zero-voltage switching, and high DC-link current utilization, which reduces switching losses and electromagnetic interferences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current source inverters (CSIs) are used instead of voltage source inverters (VSIs), then common-mode voltage generation is reduced and short-circuit immunity is improved, but conduction losses increase and conversion efficiency decreases
Solution Approach 1:
The patent implements dynamic switching of the CSI bridges using PWM control, allowing the inverter to operate in different modes (active, freewheeling, resonance) to optimize performance. The dynamic control enables the system to achieve soft-switching conditions that reduce conduction losses while maintaining the inherent short-circuit immunity of CSI topology.
Solution Approach 2:
The patent changes the operating parameters of the CSI by introducing resonant tanks that operate at specific frequencies. By controlling the switching frequency and duty cycle, the system achieves zero-voltage switching (ZVS) conditions that reduce conduction losses while maintaining the reliability benefits of CSI architecture.
2Loss of energy
If conventional VSIs are used for motor drives, then conversion efficiency can be maintained, but large short-circuit currents are generated and DC-link capacitor size increases
Solution Approach 1:
The patent divides the DC-link energy storage function between the inductor and capacitor, with the inductor handling the bulk of the energy storage and the capacitor providing only ripple filtering. This segmentation allows the use of smaller capacitors while maintaining efficient operation and preventing large short-circuit currents through the inherent current-limiting property of the inductor.
Solution Approach 2:
The patent introduces resonant tanks as intermediary circuits between the DC-link and the motor, which act as buffers during switching transitions. These resonant circuits smooth current transitions and prevent large short-circuit currents while maintaining efficient power conversion through controlled resonance.
3Loss of energy
If CSI operates at lower switching frequencies, then conduction losses are reduced, but dynamic performance deteriorates and passive element size increases
Solution Approach 1:
The patent employs periodic resonant switching cycles that include active phases, freewheeling phases, and resonance phases. This periodic operation at optimized frequencies allows the system to achieve both low conduction losses during freewheeling and good dynamic performance during active power transfer phases, resolving the trade-off between switching frequency and losses.
Solution Approach 2:
The patent ensures continuous useful action by implementing interleaved operation of multiple CSI bridges, where one bridge is in active phase while another is in freewheeling phase. This continuity allows the system to maintain high dynamic performance without requiring high switching frequencies, as the power transfer is never interrupted.
4Loss of energy
If wide-bandgap devices like SiC are used in VSC, then switching losses are reduced and operating temperature increases, but switching dv/dt increases causing additional EMI and motor losses
Solution Approach 1:
The patent uses resonant vibration at controlled frequencies to enable soft-switching operation. By operating the CSI bridges at their resonant frequencies, the system achieves zero-voltage switching that eliminates the high dv/dt associated with hard switching, thereby reducing EMI and motor losses while maintaining the low switching losses benefit of wide-bandgap devices.
Solution Approach 2:
The patent converts the inherently high switching speed of wide-bandgap devices, which causes EMI, into a benefit by using it to drive the resonant tanks. The high dv/dt is channeled into the resonant circuits where it creates controlled oscillations that enable soft-switching, thereby transforming the harmful EMI into a useful mechanism for loss reduction.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The SSCSI achieves higher conversion efficiency, reduced DC-link inductance, lower EMI generation, and improved dynamic performance, retaining the benefits of CSIs like bi-directional power flow and lower common-mode voltage generation while overcoming their efficiency and conduction loss limitations.
Implementation Method 1
a resonant tank can be connected in parallel with the DC-link inductor. The resonant tank can provide zero-voltage switching conditions for each switch of the first and second CSI bridges
Implementation Method 2
The DC-link inductor can be connected in series between the first and second CSI bridges
Data Source
AI summary
The present disclosure relates to current source inverters (CSIs), and in particular to soft-switching current source inverters (SSCSIs). An exemplary CSI comprises a first CSI bridge, a second CSI bridge, a DC-link inductor, and a resonant tank. The first CSI bridge can be operatively connected to a first power bank. The second CSI bridge can be operatively connected to a second power bank. The DC-link inductor can be connected in series between the first and second CSI bridges. The resonant tank can be connected in parallel with the DC-link inductor.